Koh Bon

Verified2026-09-30 checkedReefWallDrift

The manta ridge of the Similans, where they queue at a cleaning station.

Depth: 10–35 m33–115 ft
Difficulty: Intermediate
Entry: Liveaboard · Boat
Typical current: Moderate
Coordinates: 9°7.998′N 97°46.998′E
Activities: Scuba · Freediving

Koh Bon is a limestone island north of the Similans with a ridge running west off its southern tip, and the ridge is a cleaning station. Reef mantas come in from February to April and hold position over the rock while wrasse work them, which means a diver who finds a hole out of the current and stays in it can watch for the whole dive. Nobody chases: a manta leaves when it is approached and the next group gets nothing. The rest of the site is a hard coral wall with trevally running the edge.

Liveaboard or day boat from Khao Lak, four hours. The park closes mid-May to mid-October.

Best season

ExcellentDec–Apr
GoodNov

Before you get in

Past 30 m, where no-stop time and gas both go quickly and nitrogen narcosis starts to show.
A wall. There is no bottom in sight to judge against, so depth is kept by the gauge alone — and it is easy to end up deeper than intended.
A drift dive: you do not come back to where you went in, so boat pickup and an SMB are part of the plan rather than extras.

Taken from this site’s recorded depth, type and current, and nothing else. An empty list is not a safe site — the sea on the day, the local geography and the boat traffic are not in it. The briefing on the spot comes first.

Conditions

Water temperature: 29.6°C85°F
Wave height: 0.3 m1 ft
Air temperature: 28.1°C83°F
Wind speed: 3.4 km/h2.1 mph

Updated 2026-10-07 15:45 UTC · Source: Open-Meteo

Weather data by Open-Meteo.com (CC BY 4.0)

Conditions are reported for information only. Assess the site yourself and follow your guide and your training.

No live conditions for this site yet.

We only show numbers we can attribute to a source.

Sea state and tide

On a date

Tide · 10/7

Low01:10-0.16 m
High07:181.25 m
Low13:43-0.41 m
High19:541.30 m

Forecast heights against mean sea level. Real tides in a bay, a harbour or over a flat can differ — check an official tide table before you get in.

Pick a day to see its tide

Only wave height and wind are scored, because those are what close a boat ramp or a shore entry. Water temperature is reported and never scored: 12°C is an ordinary dive in a drysuit and punishing in a 3 mm, and a number that cannot see your suit has no business marking it down. Stars do not decide whether you get in — you and your guide do, on the day.

Weather data by Open-Meteo.com (CC BY 4.0)

Marine life you may see

Reef manta rayMobula alfrediFeb–AprSeasonal
Bluestreak cleaner wrasseLabroides dimidiatusCommon
Moorish idolZanclus cornutusCommon
Titan triggerfishBalistoides viridescensCommon
Bluestripe snapperLutjanus kasmiraCommon
TrumpetfishAulostomus chinensisCommon
Staghorn coralAcropora spp.Common
Bigeye trevallyCaranx sexfasciatusCommon

From divers

What people who were in the water reported. Not a forecast, and not a judgement about whether the site is safe to dive.

No recent reports from divers. If you dived here in the last two weeks, you can say how it was.

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